The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The double-flow turbojet engines have a first envelope and a second envelope, one inside the other, limiting respectively a pressurized cold flow which is established between the first and second envelopes and a hot flow which is established inside the second envelope. The cold flow is most often generated by a fan disposed at the inlet of the jet engine. The hot airflow is composed from a portion of the cold air having passed through the fan and by the combustion gases of at least one combustion chamber disposed inside the second envelope which drives a turbine, the shaft of which drives the fan.
In propulsion mode, the two flows come together at the nozzle outlet.
In thrust reverse mode, by a mechanism that is not implemented in the context of the present disclosure, a more or less high fraction of the cold flow is returned upstream of the turbojet engine, thus applying a thrust in the reverse direction of the jet engine advance.
As a result, the cold flow has turbulences which it is important not to increase or even to reduce on one hand, and the propagation of the acoustic noises resulting therefrom must be filtered as much as possible.
In the state of the art, it is known to make mechanical structures, such as panels and crossbars, in form of cellular composites, each cell behaving substantially as a Helmholtz resonator.
The present disclosure relates to the improvement of the acoustic absorption characteristics of the structures that are located in the air flow of an aircraft nacelle, such as radial splitters, but also others.
Conventionally, such structures are formed by panels of cells (“honeycombs”), covered with an aerodynamic outer skin drilled with holes allowing to form Helmholtz resonators, having an acoustic attenuation effect.
By nature, these structures must have a small thickness, in order to limit the aerodynamic impact on the air flow.
Thus, when seeking to improve the acoustic performances of these structures, it is not possible to increase the depth of the cells without damaging the aerodynamic performances.